1. Field of the Invention
The present invention relates to an image-processing device and a method for controlling the device, particularly to an image-processing device and a method for controlling the device, using a method for changing magnifications in a sub-scanning-direction (carriage moving direction) when reading an image by conventionally changing carriage moving speeds and a method for changing magnifications in a sub-scanning direction through a combined operation in an image-forming device using a charge coupled device (CCD) as a photoelectric-conversion device for reading an image in a scanner section.
2. Description of the Related Art
As is publicly known, image-processing devices such as an electronic copying machine, digital copying machine (PPC), and facsimile use a CCD or the like by mounting it on a scanning carriage as a photoelectric-conversion device for reading an image in a scanner section.
Thus, in a optical system of a scanner section for reading image data by using a CCD or the like, the size (magnification) of a read image is decided by the number of pixels of a CCD used or the magnification of a lens used in the main scanning direction.
Therefore, a method is widely used which is performed by operating a digital signal obtained by A/D-converting an image signal read by a CCD as a technique for changing magnifications after reading.
In a sub-scanning direction (carriage moving direction), the following method is used: a method for changing magnifications by changing moving speeds of a carriage and thereby changing document widths to be read in one main scanning line or a method for changing magnifications through operations after reading the image data of one page.
However, in the case of the method for changing sub-scanning directions by changing moving speeds of a carriage, when a magnification ranges between 25 and 400%, a moving speed at 25%, 16 times larger than the moving speed at 400% is necessary when considering the moving speed of the carriage.
Moreover, when a CCD used is a four-line CCD capable of reading a monochrome signal and a color signal, the light-receiving sensitivity of a monochrome signal is different from that of a color signal.
Therefore, the carriage moving speed for reading a monochrome signal becomes different from the carriage moving speed for reading a color signal depending on the light-receiving sensitivity of each signal.
For example, when the difference between light-receiving sensitivities of a monochrome signal and a color signal is four times, a four-times speed difference occurs between the monochrome signal and the color signal for read at a magnification of 100%.
The difference is shown below by a specific value. That is, when the carriage moving speed at 100% of a monochrome signal is equal to 200 mm/sec, the carriage moving speed at 100% of a color signal becomes 50 mm/sec.
Similarly, the carriage scanning speed at 25% of a monochrome signal becomes 800 mm/sec.
Thus, it is necessary to change carriage-scanning speeds in a wide range of 64 times in accordance with the magnification-change rate of each of a monochrome signal and a color signal in the case of the above example.
To realize the above, it is necessary to select a motor which can be operated in the speed change range of 64 times as a motor for driving a carriage and take measures for vibrations effective throughout the whole speed range.
In this case, a problem occurs that the total cost of an image-forming device increases.
Moreover, in the case of a color CCD for reading RGB signals, an interval of several lines is physically produced between R and G and between G and B. Therefore, it is necessary to perform line correction as line alignment of RGB signals.
For example, when line intervals between RGB are respectively 8 lines, a memory for a delay of 16 lines is necessary for 100% read.
Moreover, to correspond to sub-scanning-directional enlargement in accordance with 25 to 40% of a magnification change by a carriage, a memory for a delay of 64 lines is necessary and moreover, a circuit for correcting one line or less is necessary.
These memory and circuit also cause a problem that the total cost of an image-forming device is increased.
To reduce vibrations in the whole speed range, the Jpn. Pat. Appln. Publication No. 77980/2001 discloses a system for changing magnifications in a sub-scanning direction by combining change of specific magnifications according to a carriage scanning speed with a reduction operation.
That is, this system changes only specific magnifications in a sub-scanning direction in accordance with a carriage scanning speed and changes magnifications with a reduction operation technique for a magnification (magnification designated by a user) not coinciding with the specific magnification.
However, because this system performs magnification change processing of all magnifications not coinciding with specific magnifications only by the reduction operation technique, image quality deterioration such as skip or moire of a thin line or diagonal line may occur when reducing a specific magnification from 200% to 101%.